1. Field of the Invention
The present invention relates to a recording paper turning-over apparatus, and in particular, to an automatic recording paper turning-over apparatus, equipped in an image forming apparatus, employed for automatically turning-over recording paper in order to form images on both surfaces of recording paper.
2. Discussion of the Background Art
An image forming apparatus for forming images on both surfaces of a recording paper, that is, an image forming apparatus having a so-called both-surfaces image forming mode, is well known. Such an image forming apparatus is equipped with a recording paper turning-over apparatus for automatically turning-over the recording paper in order to form images on both surfaces of the recording paper.
For instance, the published specification of Japanese Laid-Open Patent Publication No. 8-59046/1996 describes a construction in which a pinch roller of a nip release roller apparatus, capable of being normally and inversely driven, is provided to be releasably attached to and detached from a driving roller. An operation of releasing the pinch roller in the nip release roller apparatus is performed in accordance with information from a recording paper detecting unit disposed at a predetermined position.
However, in the above-mentioned background apparatus, unevenness of a pressurizing force in the back-and-forth direction or in the axis direction perpendicular thereto in relation to the recording paper transporting direction tends to occur easily when the pinch roller is brought into contact with a paper turning-over roller. As a result, a high precision for assembling parts of the apparatus is required, and the cost of assembling the parts, including the noted rollers and other parts such as a sensor, a motor employed for rotating inversely, a changing-over claw, etc., is inevitably raised. Furthermore, a waiting time for adjusting a timing is lost, and therefore the above apparatus is not suitable for performing an operation of both-surfaces printing with high speed.